
where \({\bf q}_i \sim \mbox{$\mathcal {C}$}\mbox{$\mathcal {N}$}({\bf 0}, {\bf C}_{{\bf q}_i{\bf q}_i})\)  is the quantization noise vector at BS\(_i\)  with its covariance matrix of [1]}
\({\bf C}_{{\bf q}_i{\bf q}_i} = \alpha \beta {\rm diag}\big ({\bf W}_i{\bf W}_i^H\big ).\) 
